Six Cylinder 4.2 Liter Jeep engine Specs

[TerryMason]

The popular AMC 258 inline 6 4.2L engine was introduced back in 1971, and was used in various pickups and Wagoneers. In 1972 the engine was avaliable in Jeep CJs, and eventually made it's was into Wrangler YJs until it was phased out. This engine produced gobs of torque, was reliable, and inexpensive.

The carburetor (Carter BBD) that was chosed for this system, and it soon became very unpopular. It used a pulse air system that was a mess of air hoses.

 

[TerryMason]

Six Cylinder 4.2 Liter Jeep engine Specs - Technical specs

<TABLE cellSpacing=0 cellPadding=2 width="100%" border=1><TBODY><TR><TD width="33%">Displacement</TD><TD align=middle width="33%">256 cubic
inches
</TD><TD width="34%" rowSpan=11>

Click below to see
the Vacuum curve​

​

</TD></TR><TR><TD width="33%">Cylinder numbers (front
to rear)
</TD><TD align=middle width="33%">1-2-3-4-5-6</TD></TR><TR><TD width="33%">Firing order</TD><TD align=middle width="33%">1-5-3-6-2-4</TD></TR><TR><TD width="33%">Spark Plug gap</TD><TD align=middle width="33%">0.033 to
0.038
</TD></TR><TR><TD width="33%">Ignition timing</TD><TD align=middle width="33%">9 to 11
degrees
</TD></TR><TR><TD width="33%">Idle speed (auto)</TD><TD align=middle width="33%">600 +/-
70 rpm
</TD></TR><TR><TD width="33%">

(manual)​

</TD><TD align=middle width="33%">680 +/-
70 rpm
</TD></TR><TR><TD width="33%">Engine oil</TD><TD align=middle width="33%">API SE of
SF
</TD></TR><TR><TD width="33%">- Oil capacity</TD><TD align=middle width="33%">6qts</TD></TR><TR><TD width="33%">Automatic
Transmission Fluid
</TD><TD align=middle width="33%">Mercon
ATF
</TD></TR><TR><TD width="33%">- ATF Capacity</TD><TD align=middle width="33%">4qts</TD></TR></TBODY></TABLE>

<TABLE cellSpacing=0 borderColorDark=#999966 cellPadding=0 width="100%" borderColorLight=#cccc99 border=1><TBODY><TR><TD align=middle bgColor=#ffff66 rowSpan=2>Engine</TD><TD align=middle bgColor=#ffff66 rowSpan=2>Transmission</TD><TD align=middle bgColor=#ffff66 colSpan=2>Initial
Timing at


Curb Idle (Vacuum
Hose

Disconnected)
</TD><TD align=middle bgColor=#ffff66 colSpan=2>

Curb
Idle Speed RPM​

</TD></TR><TR><TD align=middle bgColor=#ffff66>Set
To
</TD><TD align=middle bgColor=#ffff66>Acceptable

Range
</TD><TD align=middle bgColor=#ffff66>Set
To
</TD><TD align=middle bgColor=#ffff66>Acceptable

Range
</TD></TR><TR><TD align=middle rowSpan=6>258

1 Barrel carb
</TD><TD align=middle rowSpan=3>Manual</TD><TD align=middle>3°

(49)
</TD><TD align=middle>1°

5°
</TD><TD align=middle>850

(49)
</TD><TD align=middle>750

950
</TD></TR><TR><TD align=middle>10°

(Alt)
</TD><TD align=middle>8°

12°
</TD><TD align=middle>600


(Alt)
</TD><TD align=middle>500

700
</TD></TR><TR><TD align=middle>8°

(Cal)
</TD><TD align=middle>6°

10°
</TD><TD align=middle>850

(Cal)
</TD><TD align=middle>750

950
</TD></TR><TR><TD align=middle rowSpan=3>Automatic</TD><TD align=middle>8°

(49)
</TD><TD align=middle>6°

10°
</TD><TD align=middle>550

(49)
</TD><TD align=middle>450

650
</TD></TR><TR><TD align=middle>10°


(Alt)
</TD><TD align=middle>8°

12°
</TD><TD align=middle>550

(Alt)
</TD><TD align=middle>450


650
</TD></TR><TR><TD align=middle>8°

(Cal)
</TD><TD align=middle>6°

10°
</TD><TD align=middle>550

(Cal)
</TD><TD align=middle>450

650
</TD></TR><TR><TD align=middle rowSpan=2>258


2 Barrel carb
</TD><TD align=middle>Manual</TD><TD align=middle>6°</TD><TD align=middle>4°

8°
</TD><TD align=middle>650</TD><TD align=middle>550

750
</TD></TR><TR><TD align=middle>Automatic</TD><TD align=middle>6°</TD><TD align=middle>4°


8°
</TD><TD align=middle>550</TD><TD align=middle>450

650
</TD></TR></TBODY></TABLE>

 

[ricroz]

Coverted my 1986 AMC Eagle to Howell TBI fuel injection last year. Ended up with a much better running engine and a garbage can full of useless hoses and emmisions control junk. I understand AMC was about to move all it's cars to FI when the company folded in 88.

 

[carnuck]

They had TBI in '86 (My Comanche 2.5L has it) and were about to put it into the Eagle SX4s but when Chrysler took over, they nixed the idea and designated the AMC version of the Eagle to the trash pile, then sold the name to Eagle Mitsubishi a couple years later.

The AMC 6 cyls had 2 different bell patterns that changed in '72 to match the AMC V8s. Prior to that they had their own small pattern and '71 is the only year for 258s with the small pattern (they lived on in Industrial use and Postal trucks a few years more)

In '71 the block was made taller for a longer stroke. The 258 is the early 232 with a longer stroke. The '71 up 232 is a 199 with longer stroke. They did the same thing with the V8 motors.
343 became 360, 290 became 304 and 390 came out, they modified the block (extra webbing and beefing up) to make the 401.

The 258 had 2 other relatives besides the 232. In Mexico they had a 282 and a 262 made by making the bore larger (new block)

 

[DIRTY-CJ]

Yuk! I have the 258 I-6... I went witrh the offenhauser intake mani, Holly truck avenger (I jetted it down to about 270) pacesetter headers with magna flo exhaust. It now runs like a raped ape I love it!

 

[Buck hour]

Yuk! I have the 258 I-6... I went witrh the offenhauser intake mani, Holly truck avenger (I jetted it down to about 270) pacesetter headers with magna flo exhaust. It now runs like a raped ape I love it!

How much was the avenger and where did you get it from?

 

[atlasfos]

I have a question about the 4.2L I6. I noticed TerryMason posted specs for auto and manual trannies for that engine. Does anyone happen to know what automatic transmission bolts to that. I have a 1990 Wrangler YJ. Transmission went out and all i am finding are manuals. Any info would be great! THANKS

 

[elevatorman]

Chrysler TF 999.
I have a 1987 and my buddy has a 1990 . Both are automatics and both have the same trans.
I had done some research last year and this is the one that was listed. Used mostly by Chrysler in medium sized trucks and jeep